1. Field of the Invention
The invention relates to an adjustable hydraulic damper with a damping piston which is secured on a hollow piston rod and divides the working cylinder into two chamber halves filled with damping fluid and has at least one throttle member, a constant oil passage being present through a transverse bore arranged above the damping piston and the interior of the piston rod, and for adjusting the damping force, an axially displaceable tension rod is arranged in the interior of the piston rod and is connected to an electro-magnet comprising a coil and an armature.
2. Description of the Prior Art
An hydraulic damper is disclosed in DE-OS No. 29 11 768, in which regulation is achieved by an electro-magnet and by which the adjustment of the damping force is possible at low piston speeds. A drawback in this arrangement is that no change in the damping force is possible at medium and high piston speeds. Moreover, no change in the valve force at medium piston speeds is possible since the piston rod simply acts to hold a corresponding by-pass open or closed.
In order to adjust damping forces at low and medium piston speeds, a variable oil pressure technique has been proposed in DE-PS No. 894 965. In such a construction, in additon to the change in the cross-section of the passage, the pre-loading of the valve spring is altered by means of oil pressure, for which, in a disadvantageous manner, throttle setting devices and corresponding pipe systems are necessary.